1. Field of the Invention
The present invention relates to a suck back valve in which liquid dripping, for example occurring at a supply port of a fluid passage, is prevented by sucking a predetermined amount of fluid flowing through the fluid passage by displacement of a diaphragm, yet wherein the sucked amount of fluid can be stabilized.
2. Description of the Related Art
There has hitherto been known, for example, a semiconductor wafer manufacturing process in which a suck back valve is employed. In the suck back valve, when supply of coating liquid to the semiconductor wafer is halted, there is a function for preventing so called liquid drip, wherein minute amounts of coating liquid drip from a supply port onto the semiconductor wafer.
The suck back valve according to such a conventional technique is shown in FIG. 5 and is disclosed, for example, by Japanese Utility Model Publication No. 8-10399.
Such a suck back valve 1 comprises a main valve body 5 formed with a fluid passage 4 interconnecting a fluid inlet port 2 and a fluid outlet port 3, and includes a bonnet 6 connected to an upper portion of the main valve body 5. A diaphragm 7 made up of a thick-walled portion and a thin-walled portion is disposed in the center of the fluid passage 4. An unillustrated pressurized fluid supply source is connected to the bonnet 6, the bonnet further being formed with a pressurized fluid supply port 8 for supplying pressurized air for operating a diaphragm under a switchover action of a directional control valve (not shown).
A piston 9 is fitted to the diaphragm 7, with a v-packing 10 installed in the piston 9 and slidable along an inner wall surface of the main valve body 5 and serving a sealing function. Further, a spring 11 which normally presses the piston 9 in a upward direction, is disposed in the main valve body 5.
An adjusting screw 12 is disposed on the top of the bonnet 6 which, by increasing or decreasing a screw-in amount thereof, abuts against the piston 9 and adjusts a displacement amount of the piston 9, whereby the amount of coating liquid sucked by the diaphragm 7 is adjusted.
A coating liquid supply source 13 storing therein a coating liquid is connected to the second fluid inlet port 2 through a tube 14, and further, a directional control valve device 15 made up for example by an ON/OFF valve which is constructed separately from the suck back valve 1 is connected between the coating liquid supply source 13 and the fluid inlet port 2. By energization and deenergization thereof, the directional control valve device 15 serves a function of switching between a coating liquid supply condition and a supply-halted condition with respect to the suck back valve 1.
Operation of the suck back valve 1 shall now be explained in outline. In an ordinary state in which the fluid is supplied from the fluid inlet port 2 to the fluid outlet port 3, the piston 9 and diaphragm 7 are displaced downwardly in an integrated manner in accordance with action of the pressurized fluid supplied from the pressurized fluid supply port 8. The diaphragm 7, which is coupled to the piston 9, protrudes into the fluid passage 4 as shown in FIG. 5 by the two-dot-chain line.
At that point, under a switch-over operation of the directional control valve device 15, the flow of coating liquid in the fluid passage 4 is halted, and in that case, by halting the supply of pressurized air from the pressurized air supply port 8, the piston 9 and diaphragm 7 are raised in unison by an elastic force of the spring 11, whereby any coating liquid which remains inside the fluid passage 4 is sucked under a negative pressure action of the diaphragm 7, preventing unwanted liquid dripping from occurring at an unillustrated supply port.
Incidentally, in the suck back valve 1 according to this conventional technique, a separately constructed directional control valve device 15 is disposed between the coating liquid supply source 13 and the suck back valve 1, wherein by means of an ON/OFF operation of the directional control valve device 15 through a driving device 16, the coating liquid inside the fluid passage 4 of the suck back valve 1 is supplied, or alternatively, supply thereof is halted.
Notwithstanding, in the suck back valve 1 according to this conventional technique, pipe connecting operations between the suck back valve 1 and the directional control valve device 15 become necessary, adding complexity to the system, and in addition, the directional control valve device 15 and the driving device 16 for causing an ON/OFF operation thereof, must be provided externally of the suck back valve 1. As a result, a dedicated space for connection of the directional control valve device 15 and the driving device 16 becomes necessary, increasing the overall installation space, and resulting in the disadvantage of soaring equipment costs.
Further, fluid passage resistance is increased due to pipes which are connected between the suck back valve 1 and the directional control valve device 15, with the disadvantage that response accuracy (responsiveness) of the diaphragm 7 is deteriorated.